The present invention relates generally to equipment for processing scrap metal, and more particularly to equipment for compressing scrap metal strip into a more densified form.
Scrap metal strip is a residual by-product of manufacturing operations in which, typically, a coil of metal strip (e.g., a coil of steel strip) is subjected to a series of processing steps which may include slitting the edges of the strip and stamping pieces from the strip. The resulting residue includes a multiplicity of pieces having different contours and sizes: long pieces, both tangled and untangled; shorter pieces; skeletal pieces; sheet-like pieces; and rejected or defective stamped pieces.
Almost all scrap metal strip from manufacturing operations is recycled as part of the raw material to make new metal. In the case of scrap steel strip, it is part of the raw material charged into steel-making furnaces, of which there are two main types: the electric arc furnace in which most or all of the charge is steel scrap; and the basic oxygen furnace in which steel scrap is generally about 25-30% of the charge.
Scrap metal strip is typically light gauge (i.e., thin), and a given volume of uncompressed scrap metal strip has a relatively low density, too low to be a desirable part of the charge for a metal-making melting furnace, which requires a more compact, more densified charge. The percentage of recovery of new metal from scrap, when the scrap is melted in a metal-making furnace, depends in part on the compactness and density of the scrap metal in the charge.
To overcome the deficiency described in the preceding paragraph, scrap metal strip is typically compressed into bales which are compact, densified cubes of material. In the case of scrap steel strip, a bale thereof can have cross-sectional dimensions of 40×40 cm (16×16 in.) and a length of 60 cm (24 in.). Bales of other light gauge steel scrap can have cross-sectional dimensions of up to 60×60 cm (24×24 in.) and a length up to 150 cm (60 in.).
In addition to improving the recovery percentage of the scrap metal strip when it is melted, the bales facilitate the handling, storage and transportation of the scrap metal strip.
The current commercial process employed to compress scrap metal strip into bales is a batch operation in which a discrete volume of scrap is processed into a bale, after which a second discrete volume is subjected to the same processing operation in the same apparatus. The processing of the second volume cannot begin until the processing of the first volume has been completed (a delay, typically, of one minute or more). A more detailed description of the batch baling operation and apparatus is set forth below.
A discrete volume of scrap metal strip is loaded into a charging box which is then tipped to discharge its load into an opening in the top of an elongated, horizontally disposed compression chamber. The charging box is then returned to its loading position to receive another discrete volume of scrap, and the opening in the top of the compression chamber is closed with a hinged, hydraulically powered lid or cover which exerts a relatively small amount of vertical compression on the low density volume of scrap in the compression chamber. The scrap is then compressed, typically in two horizontal directions, each transverse to the other, by a pair of hydraulic rams movable between retracted and extended positions. One ram is extended to compress the scrap in a lateral, horizontal direction in the elongated compression chamber, and the other ram is extended to compress the scrap in a longitudinal, horizontal direction. The resulting bale is ejected from the compression chamber, the rams are retracted, the cover on the compression chamber is opened and the above-described sequence of processing steps is repeated on a new, discrete volume of scrap metal strip.
A problem can arise when a load of scrap metal strip is discharged from the charging box into the compression chamber. The load can contain long pieces of strip, parts of which can extend outside the top opening of the compression chamber and hang out over the edge of that opening. Before one can close the hinged lid for that opening, the overhanging strip parts (i.e., the excess scrap metal strip) have to be manually cut off i.e., trimmed, typically with an acetylene torch, or other device, wielded by a member of the crew that operates the baling apparatus. This interrupts and delays the sequence of processing steps and incurs an expenditure of non-productive time, effort and money.
Because of the problem described in the preceding paragraph, and because of the employment of a batch process with its inherent limitations on productivity, the current commercial operation for compressing scrap metal strip into bales is relatively inefficient. A continuous process for compressing scrap metal strip would be desirable.
The scrap metal strip discussed above is, as previously noted, a residual by-product of manufacturing operations performed on coils of new metal, e.g., coils of new steel strip. Scrap generated as a residual by-product of manufacturing operations is known as “industrial scrap”. Another type of scrap, called “obsolete scrap,” is composed of discarded articles made of metal. Light gauge, obsolete steel scrap and some heavier obsolete steel scrap are subjected to continuous processing in an apparatus known as a “shredder”.
In a shredder, the steel scrap is flailed, by rotating, free-swinging hammers, into relatively small, fist-sized pieces that provide a compact, densified charge in a melting furnace. Obsolete steel scrap is continuously fed into a shredder along a downwardly inclined path on which is located compacting equipment which can be a pair of compression rolls or a continuous, tread-like member having a portion converging toward the path in a downstream direction. The compacting equipment reduces the volume of the obsolete scrap before the scrap enters the shredder. Shredding is essentially a continuous process.
Earlier versions of the shredder dropped whole, obsolete autos, in free fall, along a vertical path onto the rotating hammers of the shredder.
A scrap-processing apparatus known as a “logger/shear” has an elongated, horizontally disposed chamber into which is loaded obsolete steel scrap which is then compacted vertically and laterally by hydraulically powered compacting elements to form an elongated cube, or log. The log is pushed downstream through the chamber, by a hydraulic ram, toward a stationary guillotine shear which cuts the log into smaller pieces. The shear comprises a hydraulically powered upper shear blade which is raised to allow a portion of the log to be pushed downstream of the shear blade following which the blade is lowered to sever that portion from the log. The logger/shear, like the baler, processes one batch of scrap at a time.
There are steel rolling mills that produce an elongated steel product which moves in a continuous stream along a horizontal path where the elongated product is cut into shorter lengths by a traveling or flying shear. The shear is mounted in a movable housing that moves in the same direction and at the same speed as the steel product during the shearing operation. After each cut, the housing moves back to its original position in preparation for the next cut.
Balers, shredders, loggers and shears are described in detail in the following publication: Nijkerk, A. A. and Dalmijn, W. L., Handbook of Recycling Techniques, Nijkerk Consultancy, The Hague, Netherlands, 1998. This publication will hereinafter be referred to an “Nijkerk.” Relevant parts of Nijkerk, designated herein below, are incorporated herein by reference.